Metabolic Cellular Stress and its Regulatory Mechanism in Diabetic Embryopathy

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ABSTRACT Congenital malformations occur in up to 10% of babies born to diabetic women. Optimal glycemic control is difficult to achieve and maintain, and even transient exposure to hyperglycemia can cause malformations. This project is formulated on the basis of our strong preliminary data. We have found 1) hyperglycemia impairs autophagy and increases the accumulation of defective mitochondria, dysfunctional proteins and swollen endoplasmic reticulum (ER) in the developing neuroepithelium; 2) the non-toxic autophagy activator, trehalose, reverses hyperglycemia-induced autophagy impairment and neural tube defects (NTDs); 3) PKCa gene deletion, a p70S6K1 inhibitor, an ER chaperone (4-PBA) and overexpression of sirtuin 2 (SIRT2) histone deacetylase in the neural tube, all reduce hyperglycemia- induced NTDs; 4) both p70S6K1 inhibitor and SIR2 overexpression restore levels of the autophagy marker, LC3-II. We test a novel hypothesis that maternal diabetes-induced autophagy impairment causes NTD formation by disrupting cellular homeostasis leading to ER stress and apoptosis, and that maternal hyperglycemia activates p70S6K1 resulting in autophagy impairment. Restoration of autophagy by trehalose prevents hyperglycemia-induced NTDs. In addition, reduced SIRT2 and SIRT6 expression mediates the effect of p70S6K1. Aim 1 will determine whether trehalose prevents hyperglycemia-induced NTDs by correcting autophagy impairment that causes ER stress and apoptosis. We hypothesize that maternal diabetes induces aberrant changes of Atg1 and Sqsmt1 expression, which regulate autophagy, leading to autophagy impairment which induces apoptosis and NTDs, and reversal of autophagy impairment by trehalose, will restore cellular homeostasis and thus prevent diabetes-induced NTDs. Aim 2 will investigate the activation mechanism and the role of p70S6K1 in autophagy impairment and NTD formation in diabetic embryopathy. Our working hypothesis is that PKCa activates p70S6K1 which causes autophagy impairment, an increase in DNA- methyltransferases (DNMTs) and a decrease in SIRT 2 and 6 gene expression leading to NTD formation. Aim 3 will determine the underlying mechanism and the role of reduced sirt2 and sirt6 gene expression in autophagy impairment that leads to diabetic embryopathy. We will test the hypothesis that promoter hypermethylation and subsequent reduced transcription factor binding activities cause sirt2 and sirt6 gene reduction which lead to autophagy impairment by modulating the expression of Atg1 and Sqsmt1 via deacetylation of Foxo transcription factors. Our studies will provide mechanistic evidence for autophagy, ER stress, p70S6K1 and SIRT2/6 as targets for therapeutic interventions.